Multi-layer Microporous Polyolefin Membrane for Battery Separators
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Solution Overview
Problem
Microporous polyolefin membranes used in battery separators lack a balance between permeability, mechanical strength, meltdown properties, and electrolytic solution absorption and retention, particularly for lithium-ion batteries, which affects battery safety, productivity, and cyclability.
Innovation Solution
A multi-layer microporous polyolefin membrane is composed of a first microporous layer made from ultra-high-molecular-weight polyethylene and a second microporous layer with a specific pore diameter distribution, where the first layer constitutes the surface layers and the second layer is positioned between them, optimizing thickness ratios and molecular weight compositions to achieve balanced properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a microporous polyolefin membrane is used for battery separators, then permeability and mechanical strength are improved, but meltdown temperature remains low and electrolytic solution retention is insufficient
Solution Approach 1:
The patent applies composite materials by combining polyethylene and polypropylene in a multi-layer structure. The polyethylene layers provide low shutdown temperature and shutdown function, while the polypropylene layers provide high meltdown temperature and mechanical strength. This composite approach resolves the contradiction between achieving adequate mechanical strength and maintaining appropriate meltdown temperature by integrating the advantages of different materials in specific layers.
Solution Approach 2:
The patent segments the separator into multiple functional layers with distinct compositions and thicknesses. The surface layers contain polypropylene for high-temperature strength, while the inner layers contain polyethylene for shutdown function. By segmenting the separator into specialized zones, each layer can optimize its specific function without compromising the overall performance, thereby resolving the contradiction between mechanical strength and meltdown temperature.
2Productivity
If separator permeability is increased for high battery capacity, then electrolytic solution absorption is improved, but mechanical strength decreases
Solution Approach 1:
The patent segments the separator into surface layers and inner layers with different porosity characteristics. The inner layers have higher porosity (30-80%) to provide excellent electrolytic solution absorption and high battery capacity, while the surface layers have lower porosity and higher crystallinity to provide mechanical strength and dimensional stability. This segmentation allows each zone to optimize its specific function without compromising the other.
Solution Approach 2:
The patent applies local quality by giving different regions of the separator different structural properties. The surface layers are designed with higher crystallinity and lower porosity for mechanical strength, while the inner layers are designed with higher porosity for electrolytic solution absorption. This localized optimization of properties resolves the contradiction between permeability and mechanical strength.
3Reliability
If polyethylene content is increased for low shutdown temperature, then shutdown properties are improved, but high-temperature strength decreases
Solution Approach 1:
The patent segments the separator into surface layers containing polypropylene and inner layers containing polyethylene. The polyethylene inner layers provide the shutdown function at low temperatures (melting at 105-130°C) by closing pores, while the polypropylene surface layers maintain structural integrity at high temperatures (melting at 160-170°C). This segmentation allows each material to perform its optimal function without compromising the other.
Solution Approach 2:
The patent uses composite materials by combining polyethylene and polypropylene in a multi-layer structure where each material contributes its specific thermal properties. The polyethylene provides low-temperature shutdown functionality while polypropylene provides high-temperature structural support, resolving the contradiction between shutdown properties and high-temperature strength through material composition design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multi-layer membrane achieves well-balanced permeability, mechanical strength, meltdown properties, and electrolytic solution retention, enhancing battery safety, heat resistance, and storage properties while maintaining high capacity and cyclability.
Implementation Method 1
electrolytic solution absorption, and electrolytic solution retention
Data Source
AI summary
A multi-layer, microporous polyolefin membrane comprising first microporous layers constituting at least both surface layers, and at least one second microporous layer disposed between both surface layers, the first microporous layer comprising a first polyethylene resin containing 8% or more by mass of ultra-high-molecular-weight polyethylene having a weight-average molecular weight of 1×106 or more, the second microporous layer comprising a second polyethylene resin containing 7% or less by mass of the ultra-high-molecular-weight polyethylene, and having a structure in which a pore diameter distribution curve obtained by mercury intrusion porosimetry has at least two peaks, and the total thickness of the first microporous layers being 15-60% per 100% of the total thickness of the first and second microporous layers.